Variable inductance device



Oct. 30, 1934. w. J. PoLYDoRoFF I 1,978,599

VARIABLE INDUCTANCE DEVICE Filed July 1, 1951 .GOO 100 600 Patented Oct. 30, 1934 UNITED STATESA l 1,918,599 VARIABLE mDUc'rANcE DEVICE Wladimir' J. Polynorm, chicago, ni., assignmto Johnson Laboratories, Inc., Chicago, Ill., a cor-I poration oi' Illinois application' July 1, 1931, sei-m1 No. 548,171

Claims.

The invention comprehends an inductive tuning device, composed of an inductance coil and a core of finely-divided magnetic material having insulated magnetic particles, suitable for u se in 5 high-frequency selective circuits. More specically, the said device may be found advantageous when applied as an inductive coupling device between an antenna and the receiving circuit of a radio-receiving apparatus. Magnetic cores of the typeherein contemplated are described in my copending applications Serial Numbers 523,11/2 and 609,159, and in various publications both in the United States and abroad.

The invention will be better understood refer- 1| ence is made to the laccompanying drawing",

wherein- Figures 1, 2 and 3 of the invention;

Figure 4 shows a diagram of a circuit embodying the invention, and

Figure 5 indicates operating characteristics of the circuit shown in Figure 4.

Figure 1 shows one variation of the invention, wherein a movable magnetic compressed core 1 is shown in partially engaged position over a coil 2, wound on a tube 3. On the same tube is wound a high inductance coil 4, terminals from both coils being secured-to the soldering lugsg5. Figure 2 show various embodiments shows substantially the same arrangement, ex-

3o cepting that the coil 4 is wound inside of the tube 3.

When the coil 2, due to alteration of the core position relative to the coil, changes its inductance to such an extent that it produces the wide variation necessary to cover a certain band of frequencies, the coil 4 is inductively affected by the core only when the core is almost fully en- -Baged with the coil. l

It is a well known fact that antenna tuning may 40 be accomplished by inductively coupling an untuned antenna to a tuned circuit. such as is shown in Figure 4, wherein'4 is the antenna coil, 2 is the inductance, 8 is the capacitance of a tuned circuit 9, and 10 is an audion, and wherein tuning to a desired frequency may be accomplished, either by variations of the capacitance 8 or of the inductance 2. Variations of inductance may be effected by moving the core l, and tuning may also be accomplished by variations of both the .50 capacity and the inductance of the circuit. Be-

cause of varying characteristics of the lantenna. and the circuit 9 at dierent frequencies, the potential deliveredto the grid electrode of an audion 10 varies greatly with frequency variations. '55 -IfthecircultQistunedbyanironcore Land the inductance and resistance of the circuit are Changed in such a manner that the ratio is kept constant throughout the frequency band, the potential delivered to the grid of the audion it), will Astill vary, but to a considerably lesser degree than it would if the circuit were tuned by varying the capacitance 8.

Tocom'pensate for these v riations of potential with frequency, it is possib e to employ in the antenna coil 4 a largnumber of turns so that the whole antenna circuit is made resonant at a frequency somewhat lower than the lowest frequency to which the circuit Q may be tuned. In that case and when said circuit is tuned throughout the entire range of frequencies with a constant input E. M. F. at the antenna, the ratio of potential delivered to the audion 10, to the constant E. M. F. applied to the antenna, represents the total gain of potential in the antenna and the tuned circuit, and may be graphically represented by curve a of Figure 5, where the range of frequencies is taken for the abscissa. This curve shows a small gain at high frequencies, which is gradually increased as the antenna circuit approaches the resonant conditions which occur somewhere below thelowest frequency of the circuit 9.

Curve b of Figure 5 shows one feature of the 85 present invention, wherein the iniluence of the iron core, approaching thecoil 4, starts to shift vthe resonant peak of the antenna circuit towards lower frequencies, resulting in a vgradual decrease of the gain as compared with curve a.

'I'his mode of operation is particularly pronounced in an inductive tuning device, such as is shown in Figure 3, wherein the core 1 is of the inner plug type, and wherein, as the core moves inside the'coil 2, and approaches the coil 4, the 95 inductance of the latter increases andthe resonant peak of the antenna circuit is shifted to lower frequencies. Because of inadequate permeability of the central plug-type core, a metallic shielding ring 7, supported by insulating sup- `m0 ports 6, may be added to the core, to thereby decrease the initial inductance of the coil by the well known short-circuiting effect, this effect being at its maximum when the ring 'l is in the middle of the solenoidal coil 2, the shortcircuitingetfect being decreasedwhen the ring is moved to the right in the drawing. At the same time the core, being moved into the coil 2, produces an increase of the inductance. Thus, the total variation of the'inductance from its lli) coils and the core all the way out, to itsmaximum value, when the ring is entirely out of the coil and the core is all the way in, is suicient to cover the entire broadcast-frequency range. The said ring may belirregularly shaped as shown te produce desired inductance variations.

Referring to Figures 1 and 2, itis evident that the inductance variations of the coil 4, as shown fili in these iigures, are not quite suiiicient to prol duce a substantially constant gain of the antenne, coupling system within the frequency range.

However, another eiect takes place when' a core- In other Words, at the high-frequency end of the frequency range, when the antenna efficiency is lowest, the transfer of energy is greatest, and

at the lower ireduencies', when thev antenna etilciencv yamorceches the peak, the transfer of .enargv is reduced to a mnimum. 'Ihese two effects counter-balance each other throughout the range ci frequencies to such an extent that it is possible to reduce the inductance value of the coil li, so as to improve the gain at the high frequencies. such event, the gain variation of the system is as represented by curve c of Figure 5, and ana preaches a straight line.

Having thus described my invention, what claim is: A

i. A variable inductance device including a tran-simmer and a magnetic core having insulated magnetic particles movable relatively. thereto, said transformer havinga solenoidal winding and a concentrated high-inductance winding at one'end ci said solenoidal winding, the coupling between said windings being varied by invase@ 1 minimum value, with the ring in the'cen'ter ci the the relative movement of said transformer and said core.

2. A variable inductance device including a transformer and a magnetic core having insulated magnetic particles movable relatively thereto, said transformer having asolenoidal winding and a concentrated nigh-inductance winding xed at one end of said sclenoidal Iwinding, ihe relative l movement ci said transformer and said core being such as to produce a considerable change 'in the inductance of said solenoidal winding and la-coinparativelzv slight change in the induct-ance of said concentrated high-inductance winding. t

3. A variable inductance device including a transformer and s, magnetic core having insulated i magnetic particles movable relatively thereto. said transformer having a solenoidal winding and a concentrated high-inductance windingflxed at one end of said solenoidai winding, the relative movementof said transformer and said core being such as to produce a substantial change in the magnetic coupling' between said windings.

il A' variable inductance device including a transformer and a magnetic core having indivisually insulated magnetic particles movable relatively thereto, said transformer having a solenoidal winding and a concentrated high-inductance winding nxed at one end oi said solenoidal winding, the relative movement o! said transformer and said core being such as to pro- 305 duce simultaneous changes in the inductance values of said windings and` in the magnetic coupling between said windings.

5. A variable `inductance device including a transformer and means movable .relatively there-'110 to, said transformer having a solenoidal wind'- ing and a concentrated high-inductance winding dxed at one end o! said solenoid winding, said means mcluding a magnetic core having insulated magnetic particles and a metallic ring spaced therefrom, the relative movement ofv said iransiornier and said means being such as to produce desired variations in the inductances of and in the coupling between said windings.

. wmnnm s. POLYDOROFF. 20 

